1. Field of the Invention
The present invention relates to an electroluminescence display device, and more particularly, to a method of fabricating an organic electroluminescence display device.
2. Discussion of the Related Art
Cathode ray tube displays have been widely used as display devices for televisions and computer monitors. However, cathode ray tubes have large size, large weight, and high driving voltage. Therefore, flat panel displays—which are thin, light weight, and low in power consumption—have been in demand. Such flat panel displays include liquid crystal display devices, plasma display panel devices, field emission display devices, and electroluminescence display devices.
The electroluminescence display device may be categorized into inorganic electroluminescence display devices and organic electroluminescence display devices depending upon the source material for exciting carriers. Organic electroluminescence display devices have drawn considerable attention due to their high brightness, low driving voltage, and natural color images through the entire visible light range. Additionally, organic electroluminescence display devices have superior contrast ratio because of their self-luminescence. Organic electroluminescence display devices can easily display moving images due to its short response time of several microseconds and are not limited by a specific viewing angle. Organic electroluminescence display devices are stable at low temperatures, and their driving circuit can be easily fabricated because they are driven by a low voltage. In addition, the manufacturing process for organic electroluminescence display devices is relatively simple.
In general, an organic electroluminescence display device emits light by injecting electrons from a cathode electrode and holes from an anode electrode into an emissive layer. The electrons combine with the holes, thereby generating an exciton. The exciton then transitions from an excited state to a ground state to emit light. Since its luminous mechanism is similar to a light emitting diode, the organic electroluminescence display device may be called an organic light emitting diode (OLED).
FIG. 1 shows a band diagram of a related art organic electroluminescence display device. As shown in FIG. 1, the related art organic electroluminescence display device includes an anode electrode 1, a cathode electrode 7, a hole transporting layer 3, an emissive layer 4, and an electron transporting layer 5 disposed between the anode electrode 1 and the cathode electrode 7. The related art organic electroluminescence display device further includes a hole injection layer 2 disposed between the anode electrode 1 and the hole transporting layer 3, and an electron injection layer 6 disposed between the cathode electrode 7 and the electron transporting layer 5. The hole and electron injection layers 2 and 6 facilitate efficient injection of holes and electrons, respectively.
The holes are injected into the emissive layer 4 through the hole injection layer 2 and the hole transporting layer 3 from the anode electrode 1. The electrons are injected into the emissive layer 4 through the electron injection layer 7 and the electron transporting layer 5 from the cathode electrode 7. Together, a hole and an electron generate an exciton 8 in the emissive layer 4. Then, light corresponding to energy between the hole and the electron is emitted from the exciton 8.
The anode electrode 1 is formed of a transparent conductive material having a relatively high work function, such as indium-tin-oxide and indium-zinc-oxide. The light from the electroluminescence display device is observed at the anode electrode 1. On the other hand, the cathode electrode 7 is formed of an opaque conductive material having a relatively low work function, such as aluminum, calcium, and aluminum alloy.
In the related art organic electroluminescence display device, the hole transporting layer 3 is generally formed by spin coating. Here, the hole transporting layer 3 formed by spin coating is coated on the entire substrate. Thus, a process for removing unneeded portions of the hole transporting layer 3 is required. Since the hole transporting layer 3 is not photosensitive, the unneeded portions of the hole transporting layer 3 have been removed using dry ice.
FIG. 2 shows a method of patterning a hole transporting layer in the related art. In FIG. 2, a hole transporting layer 20 is formed on a substrate 10 overall. As stated above, the hole transporting layer 20 is disposed only in an image area “A” for displaying images. Therefore, a dry ice nozzle 30 having dry ice is positioned over the hole transporting layer 20 outside of the imose area “A.” Accordingly, the hole transporting layer 20 outside the image area “A” is removed by exposing the hole transporting layer 20 to the dry ice. However, the hole transporting layer 20 in the image area “A” may be damaged by the dry ice. Thus, in the above method, a suction apparatus is further required to remove the dry ice around the image area “A”. As a result, manufacturing costs are increased due to the suction apparatus.